f2fs crypto: add missing locking for keyring_key access

This patch adopts:
	ext4 crypto: add missing locking for keyring_key access
Signed-off-by: NTheodore Ts'o <tytso@mit.edu>
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/crypto_key.c

@@ -202,9 +202,11 @@ int _f2fs_get_encryption_info(struct inode *inode)
 		res = -ENOKEY;
 		goto out;
 	}
+	down_read(&keyring_key->sem);
 	ukp = user_key_payload(keyring_key);
 	if (ukp->datalen != sizeof(struct f2fs_encryption_key)) {
 		res = -EINVAL;
+		up_read(&keyring_key->sem);
 		goto out;
 	}
 	master_key = (struct f2fs_encryption_key *)ukp->data;
@@ -215,10 +217,12 @@ int _f2fs_get_encryption_info(struct inode *inode)
 				"f2fs: key size incorrect: %d\n",
 				master_key->size);
 		res = -ENOKEY;
+		up_read(&keyring_key->sem);
 		goto out;
 	}
 	res = f2fs_derive_key_aes(ctx.nonce, master_key->raw,
 				  raw_key);
+	up_read(&keyring_key->sem);
 	if (res)
 		goto out;